The specific aim of the investigation is to correlate the optimal temperature for growth with the compositions of helical and non-helical segments of 16s and 23s rRNA from selected psychrophilic, mesophilic, thermophilic, and extremely thermophilic prokaryotes. The compositions of the isolated and fractionated RNA's are being determined by ion exchange chromatography and spectrophotometric characterizations. The extents of secondary structure are being assessed by the ability of monoperphthalic acid to react with an RNA component, viz., adenine residues. In helical domains (i.e., hydrogen bonded) the adenine is less accessible than the adenine residues in the non-hydrogen-bonded regions. This condition allows an assessment of the organization of the ribopolymer.